I don't own Lord of Rings.
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There are many different worlds. Often, people from one world after their deaths would be reborn in another world. Rarely, a person travelled between the worlds without dying first. This kind of person senses when the world they were born at becomes unsuitable for him and is able to go to a new Realm. Severus Alexander Snape-Prince was one such person. After turning 19 years old, he felt a shift inside of him. The Shift changed his life forever.
Next several nights after the Shift Severus dreamed about his second world. In the dreams he learnt the Middle-Earth's languages and it's history. He saw the ways of different races and saw the way of World Changer, which he now was. World Changers were called those people, who held a capacity to influence and greatly change the world.
When he understood his future world, Severus started training himself. He went to some of the best Sword Masters and learned under their tutelage, went to Gringotts and from his inherited Prince vaults chose the best goblin made sword and a set of daggers. He read books of old, which helped him train his magic, he made quite a few Emergency Potions Kits. To be safe he went to a professional wand - crafter and had his second wand crafted as well as a staff.
After paying goblins, so they would put everything in his vaults to a wizarding space, which he learnt to make, Severus felt prepared. He hadn't got many friends, so went to say goodbyes to those he had - his previous classmate Remus Lupin, Head of DMLE Amelia Bones, Auror Kingsley Shacklebote and his fellow unspeakable Ramona Fiodermen. As expected almost all of them had tears in their eyes. During the last few years of war they had gotten close. However, they accepted his future lifestyle and bid him good and happy life. Though, Severus knew that after his first successful mission he would be able to freely trael the worlds and visit his friends.
As a World Changer, in order to travel the worlds one needed to meditate. After taking everything he was going to take to a new Realm, he sat down and started meditate. During his meditation Severus saw several worlds, but travelled into the one he dreamed. Around his meditating body flashed a brown light and he was no more.
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Author's notes
The brown light simbolizes the world he is travelling into.